1. Field of the Invention
The invention relates to a control apparatus and method of an internal combustion engine, and more particularly to a control apparatus and method of an internal combustion engine which avoids generating a torque step when switching the internal combustion engine to an idle off state (i.e., when the torque is operating in a state other than idling state) from an idle on state (i.e., when the engine is operating in a idling state) when executing control to control driving force.
2. Description of the Related Art
There is an idea that in a vehicle provided with an automatic transmission and an engine capable of controlling engine output torque independently of an accelerator pedal operation by a driver, positive and negative target driving torque that is calculated based on, for example, the operating conditions of the vehicle and the operation amount of an accelerator by the driver is realized by engine torque and the gear speed gear ratio of the automatic transmission (i.e., driving force control). Also, a control method referred to as “required driving force method” or “driving force demand method” is related to this.
For example, when the engine is in an idle on state, control is executed with engine torque in the ISC (Idle Speed Control) control range as the reference. When the engine is in the idle off state, engine torque that relies on the accelerator pedal operation amount is added to this such that the driving force required by the driver is realized.
Japanese Patent Application Publication No. JP-A-2004-176671 describes a control apparatus of an internal combustion engine, which smoothly shifts from operating in an idling state to a state other than the idling state while reliably preventing a step in the torque and a drop in engine speed. This control apparatus of an internal combustion engine is one which performs torque control based on a set target torque, and includes operating state detecting means for detecting an operating state including the speed of the internal combustion engine; target speed setting means for setting a target speed when the internal combustion engine is idling; feedback controlling means for feedback controlling a control value for setting the target torque when the internal combustion engine is idling so that the detected speed becomes equal to the set target speed; learning value calculating means for calculating a learning value of required torque while idling based on the control value that was feedback controlled; required torque calculating means for calculating, according to the detected operating state, the required torque while operating in a state other than the idling state; required torque correcting means for correcting the calculated required torque by adding the learning value; and target torque setting means for setting a target torque when operating in a state other than the idling state based on the corrected required torque.
According to this control apparatus of an internal combustion engine, when idling, the control value for setting the target torque is feedback controlled so that the speed of the internal combustion engine becomes equal to the target speed, and the learning value of the required torque when idling is calculated based on the control value that was feedback controlled. Therefore, the learning value calculated in such a manner indicates the net required torque when idling that is necessary to maintain the speed of the internal combustion engine at the target speed, i.e., that is necessary to maintain idle speed. Also, when the internal combustion engine is operating in a state other than the idling state, the required torque is calculated according to the operating state at that time, the calculated required torque is corrected by adding the learning value, and the target torque when operating in a state other than the idling state is set based on the corrected required torque. As described above, the required torque when operating in a state other than the idling state is set as the sum of the required torque that was calculated according to the operating state and the learning value indicative of the net required torque necessary to maintain idle speed. Therefore, by starting to operate the internal combustion engine in a state other than the idling state with the net required torque when idling as the base, continuity of the required torque can be ensured, which makes it possible to reliably prevent a torque step and a drop in engine speed so that a shift from operating in an idling state to operating in a state other than the idling state can be performed smoothly.
In an internal combustion engine provided with an ignition device, control is performed to advance or retard the ignition timing in order to change the output torque according to various conditions. Also, it is generally known that when the ignition timing differs, so too does the ignition efficiency such that when the internal combustion engine is in an idling state (i.e., idle on state), the relative ignition efficiency drops compared with when the internal combustion engine is in a non-idling state (i.e., idle off state). The target torque is set by adding the required torque for the idle off state to the required torque for the idle on state that takes the ignition efficiency into account in this way.
Because the ignition efficiency in the idle on state differs from the ignition efficiency in the idle off state, the command values to the actuators in the internal combustion engine that have been converted from the target torque may be excessively large or excessively small such that a torque step may occur when switching from the idle on state to the idle off state.
However, Japanese Patent Application Publication No. JP-A-2004-176671 makes no mention of this kind of difference in ignition efficiency when the engine is in an idle on state versus when it is in an idle off state.